Effect of pinching on structural resilience: performance of reinforced concrete and timber structures under repeated cycles

Abstract

This article attempts to define pinching of two structural joints, reinforced concrete (RC) and wood ones. In particular, the research outlines differences and analogies between pinching of an RC portal and a Light Timber Frame (LTF) wall. This is done by focusing on the concavity of pinching in their response under repeated cycles, which produces differences in the energy dissipation. The response of the two structural archetypes under pseudo-static and dynamic simulations is analysed using the Atan hysteresis model modification. The truncated incremental dynamic analysis (TIDA) of the two systems modelled as single-degree-of-freedom (SDOF) oscillators yielded the fragility curves, approximated by a lognormal cumulative distribution (CDF). The stability of RC under repeated cycles reveals its significant resilience compared to LTF structures. The examination of the fragility functions supports a discussion about the relation between the pinching concavity and the notion of structural resilience by introducing a robustness index ranging from 0 to 1. Ultimately, a parametric analysis of a fictitious structural system derived from the timber one by varying the concavity of the pinching path leads to the estimation of the robustness index as a function of the pinching concavity.

Experimental verification for a mechanics‐based digital cloning method predicting structural performance and damage

“…The results show that larger deformation demands, $${d}_M$$, increase pinching contribution to structural responses and delay elastic and post‐yielding behaviour, reducing the rate of elastic, $${k}_e$$, degradation 43 . More pinching deteriorates structural seismic performance, 61 where less hysteretic energy dissipation capacity leads to more extensive inelastic deformation and thus increases structural collapse risk 61,63,77–79 …”

“…Digital twins development for earthquake‐affected buildings with highly nonlinear pinched responses, as typically seen in reinforced concrete (RC) framed structures, 61–64 requires a force‐deformation hysteretic model to efficiently simulate key structural damage mechanisms, such as stiffness and strength degradation and pinching 61 . This model must be as simple as possible for maximum robustness, while its physical parameters must be theoretically and practically identifiable using HLA‐SHM results 65–67 …”

“…43 More pinching deteriorates structural seismic performance, 61 where less hysteretic energy dissipation capacity leads to more extensive inelastic deformation and thus increases structural collapse risk. 61,63,[77][78][79] Figure 10 shows the power basis functions identified under Event 1 and accurately estimating elastic, 𝑘 𝑒 , and pinching, 𝑘 𝑝 , stiffness degradation from the test structure's responses under Events 2−3. The results show pinching stiffness decreases at a higher rate than elastic stiffness in Storeys 1−5, while the elastic and pinching stiffness degradation rates are similar at Storey 6.…”

Structural performance and damage prediction using a novel digital cloning technique

“…To develop a digital twin for an earthquake-damaged building with highly pinched responses typically seen in RC frame structures, [46][47][48][49] a force-deformation hysteretic model is an essential first step. This model must efficiently simulate major nonlinear structural damage and deterioration mechanisms, such as pinching, stiffness degradation, and strength degradation.…”

“…46 In particular, buildings with more severe pinching behavior have less hysteretic energy dissipation capacity and are expected to experience larger inelastic deformation, increasing the risk of structural collapse. 46,48,[56][57][58] Figure 8 shows the power basis functions identified from SHM-HLA results for elastic, k e , and pinching, k p , stiffness reduction in the BNZ building due to Event 1. They show the identified basis functions accurately predict elastic and pinching stiffness reduction in the measured responses of the BNZ building under subsequent Events 2 and 3.…”